The present invention relates to apparatus and methods for the closing (sealing) of an open end of an xe2x80x9copenedxe2x80x9d blank for a carton such as are in common use for the packaging of juices, milk, etc., and particularly to the closure of the bottom end of the carton blank prior to filling of the carton with product.
Packaging machines of the form-fill-seal type generally involve the formation of an open-ended carton, closing of the bottom end of the carton, filling the carton with a product, and thereafter closing the top end of the carton.
The economics of form-fill-seal packaging machines is based on the throughput of cartons through the packaging machine per unit of time. Techniques for enhancing the throughput of a given packaging machine include the use of dual production lines arranged in side-by-side relationship and employing certain common components of the packaging machine, filling techniques which minimize the loss of product from the carton in the course of the carton filling operation, and others. For any given machine, if the enhancement techniques have been essentially maximized, it may become necessary to look toward minimization of the energy employed in performing one or more, or even the overall, operation of the machine. Any conservation or reduction in the energy employed in the operation of the packaging machine clearly contributes to the economic value of the machine.
In a form-fill-seal packaging machine, a carton blank commonly includes a heat-sealable layer or coating on the outer and inner surfaces of the carton blank. Closure of the bottom of the carton commonly takes the form of prefolding portions of the end side walls of the open bottom end of the carton blank inwardly toward the centerline of the blank, along prescored fold lines. This infolding operation results in a plurality of the infolded portions of the carton overlying one another, at times there being three or more layers of overlying portions of the carton end side walls. To effect closure of the bottom of the blank, these end side wall portions are heated to soften the heat-sealable layer or coating, initially infolded relatively loosely and without interbonding, and thereafter pressed, employing high pressure, into intimate overlying relationship, and cooled to the extent that the overlying end side wall portions are securely bonded to one another to close (seal) the bottom of the carton.
In accordance with one aspect of the present invention, enhancement of the overall energy consumption is effected through the use of a unique closure system for the bottom end of an open-ended carton blank. The closure system of the present invention includes a pressure pad of conventional design which is urged against the external surfaces of a plurality of loosely associated overlying prefolded end side wall portions of the bottom end of a carton blank which is disposed on a mandrel which includes a backup pad disposed within the carton and contiguous to the internal surfaces of the prefolded end side wall portions to thereby capture the prefolded end side wall portions between the pressure pad and the backup pad. The force for urging the pressure pad initially against the loosely associated overlying prefolded end side wall portions and thereafter providing a sealing pressure against the infolded end side wall portions and maintain this sealing pressure for a time sufficient to permit solidification of the softened heat-sealable component of the carton blank, in accordance with the present invention, is generated by means of a piston/cylinder operating through a pivoted arm whose distal end carries a cam follower that is moved against a linearly reciprocative cam which is operatively associated with the pressure pad. Of importance in the present invention is the contour of the camming face of the cam. In this regard, the contour of the cam is chosen to provide for maximum distance of movement of the cam, at a relatively low pressure applied by the piston/cylinder, to initially urge the loosely infolded portions of the carton bottom into their desired permanent positions relative to one another, followed by minimum distance of movement of the cam at a relatively high pressure to urge the contiguous ones of the overlying infolded end side wall portions intimately against one another, and hold the same under high pressure as the heat-sealing layer or coating thereon solidifies and bonds the overlying end side wall portions together to define a closed bottom for the carton.
In accordance with one embodiment of the present invention, the contour of the camming face of the cam, is provided with a first convex curvature of a first radius of curvature and relatively short length, which transitions relatively sharply into a second and concave curvature of a second radius of curvature and relatively long length. When viewed in a side elevational view (see FIG. 7), the transition between these curves of the camming surface are both tangent to an imaginary line drawn through the transition of the two curves and being oriented six degrees from the vertical. Moreover, both the curves are tangent to one another at their transition.
For example, employing the present invention at an air pressure setting of 85 psi, for example, one can develop a sealing pad force at the pressure pad which is at least 25% greater than the sealing pad force developed by the same air pressure setting and employing a prior art xe2x80x9cin-linexe2x80x9d piston/cylinder subassembly having a bore of about 2.5 times larger. This ability to employ a smaller bore in the cylinder thus provides an enhanced sealing pressure while employing about ⅓ the volume of pressurized air.